The Epstein-Barr virus (EBV)-induced membrane antigen (MA) complex was compared in Raji cells abortively infected with P3HR-1 virus and in a cell line producing transforming EBV. To enhance MA production in the producer cell line, the cells were exposed to 40 ng/ml tumor-promotor agent (TPA) for 72–96 hr. Such treatment increased the percentage of MA-positive cells from 10 to 30–50% over this time period. Both types of cultures were surface labeled by three different but highly sensitive techniques. The cells were then solubilized with Triton X-100 and the radiolabeled EBV-specific membrane proteins were precipitated by sera containing high antibody titers to MA. Analysis of these immune precipitates on sodium dodecyl sulfate-polyacrylamide gel electrophoresis identified only one antigen of 90,000 molecular weight common to both the superinfected Raji cells and TPA-activated producer culture. In addition, four additional antigens at 300,000, 250,000, and 170,000 molecular weights were found with two of the labeling procedures to be present on the superinfected Raji cells while the TPA-activated producer culture contained only one additional high molecular weight antigen of 320,000. To determine if this difference denoted a possible strain difference or, alternatively, reflected a difference in membrane antigen production between abortive versus permissive infections, TPA-activated cells from the parent culture producing P 3HR-1 virus were also examined. Three of these proteins identified in abortively infected cells were identified in the membranes of this producer culture. The data suggest, therefore, that these differences in membrane components might reflect differences between various EBV strains.